Coconut coir pith is a by-product of the coconut husk fiber processing industry. Coir is the name given to the fibrous material that constitutes the thick mesocarp (middle layer) of the coconut fruit (Cocos nucifera). In processing, the long fibers of coir are extracted from the coconut husk for use in the manufacture of brushes, upholstery stuffing, filters, twine and like products. The short fibers (10 mm or less) and dust (collectively referred to herein as “pith”) traditionally have accumulated in large piles or “dumps” as a waste product resulting from the processing of coconut husks to obtain the industrially valuable long fibers.
It has been recognized that coconut coir pith material provides an excellent growing medium for plants and it has been suggested that coconut coir pith can provide an effective alternative to previously standard growing media such as peat moss. Coconut coir pith is very similar to sphagnum peat moss in appearance, having a light to dark brown color and consisting primarily of particles in the size range of 0.2-2.0 mm (75-90%). Unlike sphagnum peat, however, there are no sticks or extraneous matter in the coconut coir pith. Furthermore, sphagnum peat moss has a density of about 7 lbs/cu ft when fluffed (30-50% moisture content) whereas coir pith is much denser (i.e., about 43 lbs/cu ft when compressed at a ratio of 5:1 on volume to volume basis and about 12 lbs/cu ft when fluffed and having a 50-55% moisture content).
Coir pith as an amendment has many benefits for all types of soil. It increases the organic matter content and due to its high lignin to cellulose ratio, it remains in the soil significantly longer than peat. It improves water-holding capacity of sandy soils. The drainage of clay soils is improved with its inclusion due to its air porosity and agglomeration with clay particles. However, the use of compressed coir pith bricks is cumbersome for use by consumers. The entire brick must first be expanded with water for a relatively long period of time. Then, the consumer must physically fluff and mix the coir pith for complete wetting and expansion. Only then can the wet, expanded coir pith be spread on and incorporated into the soil.
As employed herein the term “coconut coir pith” is intended to refer to both the coconut husk pith and the short coir fibers which are known to provide an excellent growing medium and to provide a suitable and sustainable substitute for soilless growing media such as peat moss (sphagnum, sedge, hypnum and the like) for growing plants. Coconut coir pith has many physical and horticultural characteristics that make it an ideal growing medium for plants. Coconut coir pith has a high water holding capacity, ideal porosity, high cation exchange capacity and high stability (slow rate of degradation due to high lignin to cellulose ratio which prevents oxidation).
However, coconuts are typically only grown in tropical and sub tropical regions, while demand for the substrate is in the United States and Europe, which entails significant shipping and handling costs.
Presently, the forms in which coconut coir pith is available for import into the United States and Europe are rather limited. Due to the low bulk density of loose coconut coir pith at moisture contents acceptable for shipping, coconut coir pith has been compressed into discs, bricks, or blocks at a compression ratio typically of about 5:1 to enable economical overseas shipping costs. It has been known that compressed coconut coir pith in this form must be mechanically out-turned or exposed to water for a lengthy period to decompress the coconut coir pith before use as such or for inclusion in a consumer product. This processing step is relatively slow and requires the entire disc, brick, or blocks to be out-turned at once. Also, coconut coir pith that is outturned is either dry and dusty or wet and heavy which contributes to further processing problems. Furthermore, coconut coir pith is not commonly baled in the manner of sphagnum peat because this form is less compressed and, therefore, less economical to ship.
Attempts have been made to compress and form coir pith into pellets using pellet mills or extruders as, for example, disclosed in U.S. Published Patent Application 2004/0025422. Those processes require use of high shear compaction methods which generate high levels of heat through friction. Such high temperature processing alters the physical properties of the coconut coir pith substrate. The pellets produced have been found to exhibit undesirable physical characteristics such as relatively slow expansion after compaction, and the coconut coir pith normally does not expand back to its pre-compacted volume after such compaction.
For example, the use of pellet mills or extruders for compaction of coir into small compressed particles has been suggested heretofore. However, pellet making processes use high pressure to extrude the material through small orifices. Unlike roll compaction, pelletizing is a high shear process that produces significant friction and heat in the material. The friction and heat from this process may produce a coir pith pellet with undesirable physical and horticultural properties. Although comparable compression ratios can be achieved, the expansion ratio after the addition of water, water holding capacity of the material, and the rate of expansion of the granules may be reduced.
Accordingly, it is an object of the present disclosure to provide more convenient forms of coconut coir pith for horticultural use which expand rapidly upon contact with moisture.
It is a further object to provide economically effective production methods for producing compacted granular coconut coir pith products which have the desired physical and horticultural properties necessary for final product application, for example, as growth media.